The federal risk assessment agency said authorities suspect homegrown sprouts may be behind one infection in a family in northern Germany, though it says tests so far haven’t found the bacteria in the seeds.

Authorities are advising Germans not to eat raw homegrown sprouts, pointing to suspicions that the seeds may be one cause of the country’s deadly E. coli outbreak.

Officials on Friday traced the outbreak to sprouts from a farm in northern Germany but are still puzzling over how the bacteria got there, whether through workers, seeds or by other means.

The federal risk assessment agency said authorities suspect homegrown sprouts may be behind one infection in a family in northern Germany, though it says tests so far haven’t found the bacteria in the seeds.

Authorities had already issued a wider warning against eating raw sprouts. The aggressive strain of E. coli has been blamed for 36 deaths, all but one of them in Germany.